tests: Copy stdlib tests from Kotlin/JVM

This patch copies Kotlin/JVM stdlib tests (libraries/stdlib/test)
excepting ones with explicit java dependencies. It also transforms
the tests to use them as box-tests.

backend.native/tests/external/stdlib/text/StringTest/reverse.kt

@@ -0,0 +1,9 @@
+import kotlin.test.*
+
+
+
+fun box() {
+    assertEquals("dcba", "abcd".reversed())
+    assertEquals("4321", "1234".reversed())
+    assertEquals("", "".reversed())
+}